Various products require a coating applied thereto to be baked to cure the coating so that it is fixed to the part. One example is that of circuit boards where a coating is applied and then baked. Another example relates to the powder coating of metal parts which is a relatively recent method for protecting and beautifying products. Powder coating makes a product highly chip and scratch resistant and highly chemical, petroleum and salt resistant. Powder coating has the ability to apply a thick, even coat without drips or sags and has premium insulating qualities, both electrical and thermal and also removes the cold feeling from metals. It gives a decorative finish to a product along with a protective finish which is resistant to fading. Powder coating has the ability to encapsulate products, wrap around corners, help eliminate sharp edges achieve with one high quality coat with no primer necessary and can resist abuse in low and high temperature variances. Powder coating has virtually unlimited number of colours and a wide variety of finishes.
Generally powder coating is applied to many metal products powder coatings are 100% solids coatings applied as a dry powder mix of resin and pigment and subsequently formed into a film with heat. The solid resin binder melts upon heating, binds the pigment, and results in a pigment coating upon cooling. The powder is applied either by an electrostatic spray or by passing the part over a fluidised bed of powder. In both cases the parts undergo subsequent oven heating to provide a smooth continuous film.
Powder coated materials have to be heated in an oven or the like, an example of a powder coat oven is shown in U.S. Pat. No. 5,155,335 issued October 1982 of Habaki et al wherein the oven has an inlet air shield chamber connected to a horizontal heating chamber. The oven of Habaki has a generally horizontal conveyor which is limited to one item at a time in the oven on the conveyor which is adequate for large items which need to be relatively spaced out but is not very effective for small items such as jewellery and the like.
U.S. Pat. No. 4,009,301 issued February 1977 of Heckman et al discloses a method for powder coating materials. A large apparatus is used to carry items on a conveyor through a series of steps wherein the item is powder coated and baked.
U.S. Pat. No. 5,000,985 issued March 1991 of Salisbury shows a similar method of powder coating wherein materials are carried on a conveyor through the processes.
The above patents are not effective for small objects and are relatively inefficient. it will be appreciated that the parts which are relatively small are generally suspended on the carriage from a hook or the like so that each is separate as it passes through the oven.
In U.S. Pat. No. 6,194,688 issued Feb. 27, 2001 of the present inventor is shown a novel construction of oven which comprises a housing having side walls defining a closed top end and an open bottom end, with a pair of opposed heating elements in the housing at the side walls. A carrying arrangement in the housing carries a batch of parts from the bottom end where the parts are loaded on to the carrying arrangement to the top end where the parts are baked by the heat rising from the heating element. The carrying arrangement is mounted on a guide which has a track located on respective side walls in the housing, a pair of wheel arrangements on the carrying arrangement engage each track and a cable is supported by a series of pulleys and is connected to a cable winch which is controlled by the control station for driving the carrying arrangement in the housing. The carrying arrangement has a removable rack comprising a series of hooks in which the parts are attached. The bottom end has an opening such that the carrying arrangement is accessible. The housing has insulated oven panels. The control station has an up control, a pause control, a down control, a temperature control meter and an upper holding time control. In this patent is disclosed an air blower for circulating the heated air in the oven mixing the air and making the temperature of the heat uniform.
In U.S. Pat. No. 7,365,287 issued Apr. 29, 2008 by the present inventor is disclosed a number of improvements to the above arrangement.
This oven shows significant improvements in energy efficiency and convenience of operation. However effluent gases must be extracted through a discharge duct at the top end and these can contain noxious gases and waste particles emitted in the paint curing process.
In U.S. Pat. No. 5,972,075 is disclosed a purifier for removing particles from exhaust gases where a filter is provide and is then heated to burn off the collected particles. Filter is unsuitable as it can restrict the flow of gases and residue from the processing chamber.